How to generate such landscape items as grass, driveways and sidewalks?

What you need to do is generate a site plan. From within Site mode, select Draw > Site Line > Property >
Sketch. Draw in the site perimeter. As long as all lines are connected it should automatically form a site polygon.
If not, then select Edit > Form Polygon, left click on a line and right click on another line to end. This
should connect all lines and form an editable polygon rather than just lines, which may be viewed in 3D. Driveways
and Sidewalks would be handled in the same fashion.